The present invention relates generally to assuring safe and efficient operation of a battery. More particularly, the invention relates to a system for continually assuring that a battery has a satisfactory state of health (SoH) while the battery is installed in its operating environment
A battery pack's SoH degrades with use and over time because individual cells in the battery pack lose their ability to store and deliver electrical energy with use and over time. But, the battery pack operating voltage range remains the same even with degradation in a battery's capacity. Thus, while a battery pack may appear ostensibly to be in satisfactory operational condition, the battery pack may, in fact, be on the verge of failure. In some instances such failure may produce problems beyond mere lack of performance of the battery pack. For example, because individual cells in the battery pack are not identical, the individual cells may degrade at a different rate with time and use. This may lead to a condition known as cell unbalance. A battery pack with degraded cells may still deliver a desired output. However, the degraded cell(s) may discharge or charge at a faster rate when compared with the other cells in the pack. Temperature of degraded cell(s) during operation may have more variance when compared with healthy cells and may lead to unsafe conditions such as thermal runaway.
Some battery packs are employed to deliver electrical power in applications where safety is of paramount importance. For example, numerous battery packs are used in modern “more electric aircraft” (MEA). To assure safe operation of such an aircraft, it would be desirable to provide a flight crew with a continuous report of the SOH and/or cell unbalance of battery packs on the aircraft so that the flight crew might take corrective action in the event of a report of a potential failure of a battery pack.
As can be seen, there is a need for system that enables safe use of battery packs in environments such as aircraft.